For human infants, social interactions with adults can provide various opportunities for learning and communicative development. To take advantage of such opportunities, infants must learn to control and allocate attention effectively to others’ social cues, using attentional skills that have been described under the broader term of “social attention”. While prior theories suggested that infants possess certain social attentional skills from very early in development, recent work in ecologically-relevant settings indicates that specific aspects of reciprocal social coordination between infants and their caregivers may significantly influence the development of social attention abilities, as well as the development of attentional control broadly. In my thesis, I expand upon more recent findings of infant attention in everyday social contexts, by exploring how differences in the timing (contingency) and content (spatial/semantic alignment) of adults’ social responses to infants’ behaviors relate to individual differences both in infants’ immediate visual attention patterns in social settings, and in later neurodevelopmental outcomes. Within Study 1, I demonstrate that 5-month-olds whose caregivers exhibit high ratios of attentional redirection (attempts to shift focus) in response to infants’ behaviors during naturalistic play show more distractibility in response to caregivers’ broader behaviors, as well as less visual engagement with caregivers’ held objects compared to infants whose caregivers exhibit high contingent sensitivity (joint responsiveness). Study 2 takes an experimental approach, showing that both the rate and sensitivity/redirectiveness of experimenters’ controlled responses to 6-7-month-olds’ behaviors during a social interaction interact to influence infants’ immediate attention to experimenters’ object-related actions. Additionally, Study 2 explores connections between contingency, content, and behavioral arousal, illustrating that experimenters’ rate of responding predicts infant visual indices of arousal on a subsequent vigilance task. Finally, Study 3 explores infant social attention patterns and caregiver responding among 6-10-month-olds at high risk for autism (ASD), suggesting that higher sensitive responding to vocalizations at 6-10 months predicts enhanced learning outcomes at 36 months among children who receive an ASD diagnosis. Together, these studies contribute to our understanding of dyadic influences on early attention development, and help to clarify the relative influences of temporal and spatial/semantic coordination on infant social attention and learning.